In reply to Joe McGill.

SlideShow Pro solved this problem a long time back. SSP was a powerful Flash gallery option aimed at photographers, later adapted to provide a non-Flash version for i-Devices but Apple's hatred of Flash meant the developers gave up on it sadly and SSP closed shop 1st Dec 2015.
You uploaded a single large image directly via a Lightroom Plugin [or manually] and the CMS behind the scenes spits out an image resized on the fly to fit the screen site is being viewed on and MOST importantly also sharpened to prevent the usual softness you get when shrinking images.
Any chance that methodology could be implemented?
Far easier that uploading images at different set sizes,
that may not even be the correct size most of the time.